Many attempts have been made to provide a hand operated screwdriver having a safety or guiding attachment utilized to inhibit lateral movement between the screwdriver and the screw, and to guide the blade of the screwdriver into alignment with the slot in the screw head. The prior art reveals various styles and forms of screwdriver shanks with attachments thereon which have the primary purposes of retaining the blade of the screwdriver shank in the head of the screw because lateral movement may cause injury to the operator or damage to adjacent work surfaces. Further it is desirable to retain the head of the screw within the screwdriver during placement of the screw, so that the shank of the screw may be more easily guided into places which are difficult to reach.
Examples of such prior art devices are illustrated in U.S. Pat. Nos. 1,782,448, 3,608,596, 2,756,791, 3,452,373, 3,517,714 and 723,694. Each of these patents reveals or discloses a safety screwdriver having separable attachments or multiple components designed to accomplish the above objectives. Problems inherent in these screwdrivers include the fact that they are quite expensive to produce because of the multiple components. Also, because of the multiple components there is an increased likelihood of failure or breaking of the tool during use or over a period of time. For example, U.S. Pat. No. 3,517,714 to Desbarats discloses a sleeve which is slidable along the screwdriver shank from an inoperable position wherein the screwdriver functions in a conventional manner, to an operative position over the blade which prevents the blade from slipping out of the slot in the head of the screw. Desbarats' movable sleeve is constructed of a flexible rubber material and is slipped downwardly over the blade as desired. However, because the sleeve is made of a flexible material it is likely to give under the pressure of driving a screw.
U.S. Pat. No. 3,556,184 to Wagner discloses a spring loaded device wherein the screwdriver blade is normally in a retracted position in the body, but during operation is pressed forward to engage the screwhead. However, in addition to being expensive to produce the spring-loaded apparatus may fail and permit the barrel to slip away from the screw head during operation injuring the operator or the work surface.
U.S. Pat. No. 3,608,596 to Yoho discloses a cylindrical tube including a blade extending axially therein with the terminal end of the blade being coplanar with the end of the cylindrical tube. Due to the separate construction of the blade and the cylindrical tube, if a great deal of pressure is applied to the blade in driving a screw it is quite likely that the blade will dislodge from the grooves inside the tube. Further, each time it becomes necessary to sharpen the blade, the blade will be shortened and difficult to fit within the tube without additional adjustments of the blade and/or tube.
In view of these devices and others similar thereto, applicant recognized a need for an improved safety screwdriver economically produced in a strengthened one-piece construction. The present invention is directed to such a device and includes a shank portion having a handle attached to one end and on the opposite end of the shank a hollow, axially aligned tubular extension. The terminal annular edge of the tubular extension lies in a plane transverse to the axis of the shank. An elongated flat blade is secured or integrally cast between the inner walls and base of the tubular extension. The short terminal edge of the blade is recessed inwardly a prescribed distance from the annular edge of the tube so that when the screwdriver is in use the head of the screw is concealed within the tubular extension with the blade engaged in the slot in the screw head.
In a preferred embodiment the shank portion and the tubular extension with the blade therein are cast or forged as one unit. Alternate procedures include welding or machining. This unitary construction increases the strength of the tool and decreases the cost of production. Additionally, because of the integral construction of the blade with the side walls of the cylinder there are no exposed or unsupported corners on the blade, thus significantly decreasing the necessity for sharpening. However, at any time the blade does require sharpening, the procedure may be carried out without removal of the blade from the cylinder by using an emery wheel.
It is therefore an object of the present invention to provide an improved safety screwdriver of the type having a cylindrical portion which sets over the screw head during driving to guard against lateral movement of the screwdriver.
A further object is to provide such an improved safety screwdriver having a one-piece construction which eliminates attachments or separable component parts.